1. Field of the Invention
The present invention relates to a method for examining bonded-metal by ultrasonic examination, and more particularly, to the method by which the bonding properties such as a bonding temperature, a bonding strength and the like are examined on the basis of an attenuation amount of the ultrasonic wave through a bonding interface of the bonded-metal.
2. Description of Related Art
A method for joining metals together is a process by which pieces of metals are joined together, it can be classified generally into two categories: a metallurgic joining method which gives energy locally to metals to form an atomic bonding therebetween, and a mechanical joining method which use rivets and bolts.
The metallurgic joining method is further classified into a fusion welding method, a pressure welding method, a brazing and soldering method, a diffusion bonding method.
A process of the fusion welding method is as follows. Firstly, bonding faces of base metals are heated to be fusion condition. While heating, if necessary, filler metals may be added therein. The base metals are then bonded together.
A process of the pressure welding is that a high mechanical pressure is applied to bonding faces of metals, the metals are then bonded together. This pressure welding method is classified into a cold pressure welding method, a friction welding method, an explosive welding method, a ultrasonic welding method and a resistance welding method.
A process of the brazing and soldering method is as follows. Firstly, the brazing filler metals are caused to flow into gaps between bonding faces under a fusion condition. Secondly, the metals are caused to solidify, then being bonded together. In this process, the employed brazing filler metals have a lower melting point than the base metals have.
Further, a process of the diffusion bonding method is as follows. Firstly, pieces of metals are caused to contact closely, a pressure is then applied thereto under a temperature of a melting point or less of the metals so as not to produce plastic deformation. Secondly, the metals are bonded with employing atomic diffusion produced on a bonding interface. This diffusion bonding method is classified into a solid-state diffusion bonding method and a liquid phase diffusion welding method. The former is that pieces of metals are directly contacted closely, then causing elements to diffuse under a solid-state. The latter is that insert metals having a lower melting point is put between pieces of metals, then being caused to be fused momentary and solidified by way of isothermal solidification with employing elimination of diffusion of the specified elements in a liquid phase.
The metallurgic joining method such as the diffusion bonding method, different from the mechanical joining method, enables to save material and to cut man-hour, thereby producing a joint having excellent bonding strength, air tightness and pressure tightness. In contrast, a procedure for bonding metals together is irreversible, it is therefore difficult to bond them together repeatedly after separation of the bonding. Further, there is such problem that the bonding properties, such as strength and fracture toughness, vary largely, depending on a type of deficiency of a bonding interface. A lot of factors cause such flaws.
Accordingly, in the case that the metallurgic joining method such as a diffusion bonding method requires high reliability, whether deficiency exists at the bonding interface or not, is examined after bonding. Several nondestructive examinations such as a radiographic testing, a ultrasonic examination, a magnetic particle testing and a liquid penetrant testing can be applied to the bonded-metals. In the case of mass production of the same bonded-metals, from which a part is sampled and a test specimen with a bonding interface is cut off. A destructive examination such as a tensile testing is then carried out.
However, the metallurgic joining method such as a diffusion bonding method accompanies a local heating and/or cooling of metals. Thus, a heat-affected zone with variation both a micro structure and a mechanical property is liable to be produced on vicinity of the bonding interface. Even if deficiency such as flaws, blowholes and bonding defectives is not detected, the bonding properties such as joining strength and fracture toughness may unfortunately be deteriorated.
In such case, destructive examination can be applied to samples produced on a large scale. However, it can not be applied to samples produced on a small scale such as a plant production, thus there is no method for examining the bonding properties of the bonded-metal. Further, the actual bonded-metal includes both deficiency (such as flaws, voids and bonding defectives) and a heat-affected zone. There is also no method for examining the bonding properties of such bonded-metal with achieving high accuracy.
In order to overcome such problem, for example, a procedure for bonding metals together may be standardized by a manufacturer's manual book. However, the bonding properties depend on many requirements such as design of joint, accuracy, cleanliness, a bonding temperature, a holding time, and a bonding pressure. Further, in the case of having no choice but to carry out the bonding procedure out of doors, it is influenced by a weather condition such as a temperature as well as skill of an operator. To use the manufacture's manual book is not enough to achieve high reliability for such bonded-metal which is used for such portion that requires particular high-reliability.